1. Field of the Invention
The present invention relates to a fuel cell comprising a membrane electrode assembly having a solid polymer electrolyte membrane, an anode side gas diffusion electrode disposed at one side of the solid polymer electrolyte membrane, and a cathode side gas diffusion electrode disposed at the other side of the solid polymer electrolyte membrane, and a pair of separators holding the membrane electrode assembly; and to a method for producing the same: In particular, the present invention relates to a fuel cell in which the membrane electrode assembly can be reliably sealed between the separators, and to a method for producing the same.
Further, the present invention relates to a fuel cell in which the peripheries of openings for fuel gas, oxidant gas, and coolant is reliably sealed, and to a method for producing the same.
Further, the present invention relates to a fuel cell stack whose fuel cell units can be easily replaced.
2. Description of the Related Art
In conventional fuel cells, the membrane electrode assembly comprises a solid polymer electrolyte membrane, and an anode side diffusion electrode and a cathode side diffusion electrode which are disposed at both sides of the membrane. The membrane electrode assembly is held by a pair of separators. By supplying fuel gas (for example, hydrogen gas) onto a reaction surface of the anode side diffusion electrode, the hydrogen gas becomes ionized, and moves toward the cathode side diffusion electrode through the solid polymer electrolyte membrane. The electrons produced in this process are extracted to an external circuit, and are utilized as electric energy of a direct current. Since oxidant gas (for example, air which contains oxygen) is supplied to the cathode electrode, water is generated by the reaction of the hydrogen ions, the electrons, and the oxygen.
An example is explained with reference to FIG. 17. In FIG. 17, reference numeral 1 denotes the solid polymer electrolyte membrane. A fuel cell 4 is assembled such that the solid polymer electrolyte membrane 1 is held between gas diffusion electrodes (an anode side diffusion electrode and a cathode side diffusion electrode) 2 and 3. Sheet-type gaskets 5 which have openings corresponding to the reaction faces of the fuel cell 4 are provided at both sides of the fuel cell 4. While the gaskets 5 cover the edges of the fuel cell 4 and press the edges of the fuel cell 4 using outer pressers 6, the fuel cell 4 is held between separators 7 (disclosed in Japanese Unexamined Patent Application. First Publication No. Hei 6-325777).
In the above conventional fuel cell, the gaskets 5 separate the spaces between the separators 7 and the gas diffusion electrodes 2 and 3 from the outside. Therefore, this fuel cell advantageously prevents the leakage of the fuel gas and the oxidant gas, and prevents the mixing of those gases, to thereby achieve efficient electric power generation. Variations in the thickness of the separators 7 and the gas diffusion electrodes 2 and 3 are unavoidable. Therefore, when the gaskets 5 which have varying thicknesses are combined with the separators 7 and the gas diffusion electrodes 2 and 3, the reaction force produced by the gaskets is not uniform. Thus, there is the problem that the sealing between the separators 7 and the gas diffusion electrodes 2 and 3 is not uniform.
Further, the fuel cell has an internal manifold for supplying fuel gas, oxidant gas, and coolant to the anode side diffusion electrode and the cathode side diffusion electrode. The internal manifold has a number of openings through the separators.
An example of the conventional technique will be explained with reference to FIG. 32. Reference numeral 201 denotes a solid polymer electrolyte membrane. The fuel cell 204 is assembled such that the solid polymer electrolyte membrane 201 is held by gas diffusion electrodes (an anode side diffusion electrode and a cathode side diffusion electrode) 202 and 203. The fuel cell 204 is held between separators 205 and 205.
Openings 206 which constitute the internal manifold are formed in the peripheries of the separators 205 holding the fuel cell 204. The oxidant gas, or the fuel gas supplied from the openings 206 reaches the reaction surfaces of the respective fuel cells 204.
To seal the peripheries of the openings 206, a gasket 207 is inserted between the separators 205 and makes contact with the peripheries of the openings 206 (disclosed in Japanese Unexamined Patent Application. First Publication No. Hei 6-96783, and U.S. Pat. No. 4,510,213).
The above-mentioned fuel cell has problems in that the surface pressure of the gasket 207 varies in the peripheries of the openings of the separators 205, and in that a partial bending stress acts in the peripheries of the openings.
Another conventional fuel cell will be explained with reference to FIG. 47. In FIG. 47, reference numeral 301 denotes a solid polymer electrolyte membrane 301. The fuel cell 304 is assembled such that the solid polymer electrolyte membrane 301 is held by gas diffusion electrodes (an anode side diffusion electrode and a cathode diffusion electrode) 302 and 303. The fuel cells 304 are held via carbon plates 305, which are disposed in the peripheries thereof, by separators 306 and 306. The fuel cell units are assembled such that the separators 306 are attached to the fuel cells 304 by two-side adhesive agent sheet 307, and the fuel cell units are stacked to produce the fuel cell stack (disclosed in Japanese Unexamined Patent Application. First Publication No. Hei 9-289029).
That is, the fuel cells 304 and the separators 306 are bound by the two-side adhesive agent sheet 307, and the fuel cell units are thus assembled. Then, the fuel cell units are stacked. However, there is the problem in that, when replacing either the solid polymer electrolyte membrane 301 or the separators 306, the two-sided adhesive agent sheet 307 must be separated, and this takes much labor.
Further, when the two-sided adhesive agent sheet 307 is separated, components other than the replaced component may be deformed.